Background and Significance: 40% of patients presenting with "superficial" (non-muscle-invasive) bladder cancer develop the "invasive" life-threatening form of the disease during follow up. In clinical studies, overexpression of Epidermal Growth Factor Receptor (EGFR), Ha-Ras mutation and loss of tumor suppressor gene PTEN have been associated with this phenotypic tumor transition. However, the exact molecular pathway by which these genes effectively trigger or facilitate the invasive process is incompletely understood. Our original R29 hypothesized that EGFR signaling enhances bladder tumor motility in vitro and invasion in vivo and intended to determine the signaling pathways used by EGFR in this process. Since funding of the R29 in 9/97, we have made the following important observations which support the original hypothesis and address the aims of the original application: 1) EGFR and Ras inhibition diminished the motility of invasive bladder cancer cells; 2) EGF stimulates motility in non-invasive cells via PI3K and this requires activity of Rho and Ras effector Rat; 3) In non-invasive cells, baseline RalA activity is low while invasive cells have constitutively higher activation; 4) Invasive cells have low levels of RhoGDI2 expression. Reconstitution of this gene leads to diminished motility and activity of RalA but not RhoA suggesting this gene may be the first RalGDI identified to function as an invasion suppressor; 5) Inhibition of PI3K activity via PTEN reconstitution in invasive cells with inactive PTEN, results in an inhibition of orthotopic invasion in vivo and a decrease in RhoA activity. Since the overall biology of both Ral and RhoGDI2 is poorly understood, but might be critical for regulating tumor invasion in patients with bladder cancer, we propose the Guiding Hypothesis that EGF mediates bladder tumor invasion via Ral activation. We will test this hypothesis with a matrix of technologies ranging from basic biochemistry to clinical oncology to address Ral biology in human bladder cancer. These include: 1) unique paired human bladder cancer cell lines with different invasive abilities; 2) a novel organotypic bladder model allowing in vitro study of tumor invasion; 3) an orthotopic assay evaluating the effects of candidate molecules on in vivo bladder cancer invasion; 4) transgenic and knockout mice with appropriate genetic and phenotypic profiles; 5) a human tissue bank with pathologically and clinically well characterized frozen specimens. Specific Aims: 1) Determine the role and pathobiology of Ral in bladder cancer invasion in organotypic, murine orthotopie and human tumor studies; 2) Determine the regulators of Ral activation (RhoGDI2, etc..) and their effect on intracellular Ral localization and bladder cancer nfigration and invasion; 3) Determine the protein complexes associated with Ral in vitro and in vivo, including those found in human cancer. Conclusion: Completion of these specific aims will provide biologically relevant molecular information on the signaling pathways regulating bladder cancer invasion in vivo and lead to the rational development of diagnostic and prognostic tools predicting the development of invasive disease and therapies to interfere with this process in patients with superficial bladder cancer.